The use of metallic silver as an antimicrobial has been known since ancient times. In recent years, a renewed interest has developed in the use of metallic silver as an antibiotic especially in wound dressings. This renewed interest is driven in part by the development of antibiotic-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA). Antibiotic-resistant bacteria are especially problematic since an increasing number of commonly used antibiotics are becoming ineffective. Metallic silver, which release ionic silver into the wound, is a broad-spectrum antibiotic that has been found particular effective against such resistant bacterial strains. Moreover, bacteria do not appear to develop resistance to silver as compared to conventional antibiotics.
Metallic silver is also known to exhibit wound-healing properties. Expeditious wound healing benefits the patient in terms of increased comfort and decreased susceptibility to infection and secondary injury. Examples of wound dressings incorporating metallic silver-coated fibers are those sold under the tradename Silverlon® from Argentum Medical LLC located in Roswell, Ga. Other examples of wound dressings incorporating metallic silver-coated fibers are described in U.S. Pat. No. 6,087,549 also assigned to Argentum Medical LLC.
Although metallic silver has distinct advantages, silver primarily used for wound dressings is in an ionic form (i.e., a silver salt or compound). However, the antibiotic activity provided with ionic silver from silver salts or compounds dissipate rather quickly due to the silver salts or compounds in the wound care product being dissolved by the aqueous nature of the wound environment. As a result, dressings must be replaced frequently resulting in pain or discomfort and inconvenience for the patient as the dressing is removed and replaced. Moreover, the rapid release of ionic silver can possibly lead to toxicity. Similarly, silver-containing creams (e.g., including silver sulfadiazine) must be consistently reapplied to the injured area, and the dressing must be removed for reapplication of the cream. Silver salts, as well as unbound metallic silver particles, can also irritate the skin and prolonged contact can cause localized or site-specific argyria, which is characterized by a pronounced, permanent ashen-gray skin discoloration.
As is well known in the art, a moist environment promotes wound healing. Thus, would dressings often include hydrophilic (i.e., water-absorbent) fibrous materials to maintain moisture at the wound site. One class of water-absorbent materials is alginates, which are fibrous products derived from seaweed, and is commonly used to facilitate a moist wound environment. However, a moist environment also facilitates the growth of bacteria, which slows wound healing, causes unpleasant odors and can eventually lead to serious and life-threatening infections. While bandages including water-absorbent materials (e.g., calcium alginate) help to maintain a moist wound environment, they have been known to cause adherence of the dressing to the wound site. Adherence of the wound dressing causes pain and discomfort to the patient and lengthens the time required for changing the dressing and the time required for a wound to heal.
Attempts to obviate bacterial growth in water-absorbent materials have included the incorporation of antibiotics. Metallic silver-coated fibers are not used due to their hydrophobic nature, which renders them incompatible for use with water-absorbent fibers such as calcium alginate. Thus, attempts to prepare fibrous mixtures of silver-coated fibers for wound dressings generally entail using hydrophobic fibrous materials such as polyethylene and the like as taught in U.S. Pat. No. 6,087,549.
In view of the above, it is clearly apparent that there are deficiencies with currently available wound dressings. First, there is a need for antibiotic wound dressings that use metallic silver to inhibit the growth of MSRA and other antibiotic-resistant bacteria. There is also a need for wound care products that releases silver ions over an extended period of time which alleviates the need for frequent removal or replacement of the dressing or application of silver creams. There is also a need for wound dressings that maintain a moist wound environment but reduces physical adherence to the wound site. Likewise, there is a need for wound dressings that maintain a moist wound-healing environment while inhibiting bacterial growth. Likewise, there is a need for non-irritating silver wound dressings that obviate the need of silver salts for the delivery of silver ions thereby eliminating the potential development of argyria.